Ladder-type P,S-bridged trans-stilbenes

Article abstract of DOI:10.1021/ic201116p

Phosphole-containing π-systems have emerged as building blocks with enormous potential as electronic materials because of the tunability of the phosphorus center. Among these, asymmetric P-bridged trans-stilbenes are still rare, and here an elegant and ef

Full text of DOI:10.1021/ic201116p

ARTICLE
pubs.acs.org/IC
Ladder-Type P,S-Bridged trans-Stilbenes
Wannes Weymiens, Mark Zaal, J. Chris Slootweg, Andreas W. Ehlers, and Koop Lammertsma*
Department of Chemistry and Pharmaceutical Sciences, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083,
1081 HV Amsterdam, The Netherlands
S Supporting Information
b
ABSTRACT: Phosphole-containing π-systems have emerged as
building blocks with enormous potential as electronic materials
because of the tunability of the phosphorus center. Among these,
asymmetric P-bridged trans-stilbenes are still rare, and here an
elegant and efficient synthesis toward such fluorescent molecular
frameworks is described. Fine-tuning of the photophysical properties
is attempted by enforcing the planarization of the phosphorus tripod and thus increasing the interaction between the phosphorus
lone pair and the π-system. The electronic structure of the π-conjugated frameworks is analyzed with NMR, UVꢀvis and
fluorescence spectroscopy, and time-dependent density functional theory (TD-DFT) calculations.
’ INTRODUCTION
Being neglected for decades, phosphorus has become of
interest for π-conjugated molecular frameworks.1 Especially
the phosphole ring has shown potential as a building block for
organic materials,2 as exemplified by an organic light emitting
device (OLED) based on dithienylphosphole gold chloride
complex 1 (Figure 1).3 The phosphole ring,4 with its negligible
degree of aromaticity, enables efficient conjugation over the
diene moiety while offering a handle to fine-tune the photo-
physical properties of the π-system through the λ3σ3 phosphorus
center. Recently, phospholes showed their potential in ladder-
type (hetero)aromatic rings, such as the fused thiophene-phosp-
hole-thiophene 25 and the fused heterocycles 3aꢀd6 which can
be viewed as a heteroatom-bridged trans-stilbene (Figure 1). The
rigidity of such π-conjugated systems is known to enhance the
luminescence intensity over flexible nonfused systems.7 Introdu-
cing asymmetry by employing different heteroatom bridges in
the same extended π-framework is the obvious next step to tune
the electronic features. Only recently, systems that contain such
an asymmetry are developed with, for example, P,B- and P,C-
bridges in which the phosphole ring is either alkylated as in 3c6b
or oxidized as in 3d.6c
Here we present a follow-up study on the very recently
reported one on P,S-bridged trans-stilbenes bearing trans-fused
benzo[b]phosphole and benzo[b]thiophene units8 and report on
their substituent-dependent photophysical properties. Whereas
the tuning of these properties is often accomplished by chemical
modification at the phosphorus center of the phosphole-contain-
ing π-system (e.g., oxidation, metal complexation, alkylation), we
examine the effect of the degree in which the phosphorus lone
pair participates in the π-conjugation. Namely, a pyramidal
phosphorus in the phosphole ring implies an sp3-type lone pair,
which concurs with the negligible aromaticity, but planarizing
this center should enhance the p-character of its lone pair and
thus its participation in the π-framework.9 To enforce
Figure 1. Selected phosphole-containing π-systems.
Scheme 1. Synthesis of S,P-Bridged trans-Stilbenes 6a
a (a) o-bromo-phenylboronic acid, Pd(PPh3)4, Na2CO3, 1,4-dioxane,
H2O, 100 ꢀC, 16 h; (b) 1. nBuLi, Et2O, ꢀ78 ꢀCfRT, 2 h, 2. ArPCl2,
Et2O, RT, 2ꢀ16 h.
planarization we increase the steric bulk of the substituent on
phosphorus, thereby enlarging the CꢀPꢀC angles, by means
of the phenyl, mesityl (Mes; 2,4,6-trimethylphenyl), and isityl
(Is; 2,4,6-triisopropylphenyl) substituents.
’ RESULTS AND DISCUSSION
First we describe the synthesis of the P,S-bridged trans-
stilbenes 6 with Ph, Mes, and Is as the phosphorus substituent.
Received: May 25, 2011
Published: July 27, 2011
r
2011 American Chemical Society
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Table 1. Spectroscopic Data for Phosphole-Containing
π-Conjugated Systems 6aꢀc and 7aꢀc
b
c
δ(31P)a
λabs
εb
λem
ssd
c
ΦF
compd
(ppm)
(nm)
(Mꢀ1 cmꢀ1
)
(nm)
411
408
409
411
408
409
(cmꢀ1
)
6a
316
1.80 ꢁ 104
1.21 ꢁ 104
4.64 ꢁ 104
2.13 ꢁ 104
1.66 ꢁ 104
9.04 ꢁ 103
3.20 ꢁ 103
2.77 ꢁ 103
3.33 ꢁ 103
2.42 ꢁ 103
4.92 ꢁ 103
2.57 ꢁ 103
ꢀ17.4
ꢀ29.7
ꢀ33.4
25.5
0.253
0.121
0.154
0.837
0.895
0.683
5081
4730
4536
4078
3819
3023
340 (sh)
310
6b
6c
7a
7b
7c
343 (sh)
324
345 (sh)
329
Figure 2. Absorption spectra in CH2Cl2 (10ꢀ5 M) of (a) phosphole-
containing π-systems 6a (red), 6b (blue), and 6c (green), and (b) their
corresponding oxides 7a (red), 7b (blue), and 7c (green).
352 (sh)
329
27.4
353 (sh)
329
28.1
364 (sh)
a 31P NMR chemical shift in CDCl3. b Absorption maximum in CH2Cl2
(10ꢀ5 M) and extinction coefficient. c Emission maximum and quantum
yield in cyclohexane (10ꢀ6 M) using perylene (ΦF = 94%) as standard.
d Stokes shift.
Next, the influence of these substituents on the degree of
planarizing the phosphorus center is examined by NMR,
UVꢀvis, and fluorescence spectroscopy. These sections are
followed by a computational analysis using density functional
theory (DFT). Subsequently, the corresponding oxides 7 will be
briefly discussed in the same manner.
Synthesis of P,S-Bridged trans-Stilbenes 6. We adapted the
two-step synthetic route by Baumgartner et al.,8 shown in
Scheme 1, that is based on generating fused diarylphospholes
from thiophenes.5,10,11 The higher reactivity of the R-bromine of
dibromobenzothiophene 4 is employed in a regioselective Suzuki
coupling12 with ortho-bromophenylboronic acid to give dibromide
5 in 92% yield after column chromatography (cf. lit. value of
73%).8 The two bromine substituents of 5 are perfectly aligned for
phosphorus introduction after lithiation with nBuLi. Quenching of
dilithiated 5 with the appropriately substituted aryldichloropho-
sphine introduces the phosphorus fragment to give the known 6a
(100%) and the novel P,S-bridged trans-stilbenes 6b (79%) and 6c
(100%), which were fully characterized spectroscopically.13
NMR Spectroscopy of 6. The 31P NMR chemical shifts for 6a
(ꢀ17.4 ppm), 6b (ꢀ29.7 ppm), and 6c (ꢀ33.4 ppm) show a
progressive shielding for the phosphorus nucleus with increase of
the steric bulk of its substituent (Table 1). Whereas this effect
might suggest a relationship with the hybridization of the
phosphorus center, earlier calculations on phospholes have
shown instead that an increase in phosphorus planarization,
and thus an increase in electron delocalization, is more likely
to cause a small downfield shift.14 Hence, we attribute the 31P-
shielding to a sterically induced γ-effect of the phosphorus
substituent’s ortho-methyl and isopropyl groups in analogy to
that reported for 1-isityl-3-methyl phosphole.15
Figure 3. Fluorescence (solid) and excitation spectra (dotted) of 6a
(red), 6b (blue), and 6c (green) in cyclohexane (10ꢀ6 M; λexc = 350 nm;
λem = 410 nm).
1.54 ppm (CH3)) and the other one is shielded instead (δ(1H) =
1.91 ppm (CH); 0.31/0.44 ppm (CH3)). This difference be-
tween the two ortho iPr groups is remarkable. We attribute the
i
deshielding of one of the Pr groups to the influence of the
neighboring phosphorus atom and presume that the shielded iPr
group is located above the π-system. The two methyl groups of
each ortho iPr group are chemically inequivalent, have different
i
chemical shifts, which suggests hindered rotation for the Pr
group, thereby underscoring the steric congestion of isomer 6c.
The same but less pronounced features are also present in the
1
less crowded mesityl-substituted 6b. Three different H NMR
methyl resonances are observed at 3.07, 2.25, and 1.26 ppm. The
two meta protons of the mesityl group of 6b resonate also at
different chemical shifts (7.05 and 6.62 ppm). It is speculated that
the upfield resonance is caused by the proton being in the
shielding zone of the phosphole ring.
UVꢀvis and Fluorescence Spectroscopy of P,S-Bridged
trans-Stilbenes 6. The absorption and fluorescence data of the
phosphole-containing π-conjugated systems 6aꢀc are summar-
ized in Table 1. Two absorption maxima are observed at λabs
=
258ꢀ260 nm and 316ꢀ326 nm with a shoulder 340ꢀ345 nm
(Figure 2a). Excitation at either one of these absorptions results
in a broad fluorescence band with a λem maximum at
408ꢀ411 nm (Figure 3) with quantum yields ranging from
0.121 to 0.253, which are higher than analogous phosphole-
containing bridged trans-stilbenes (cf. ΦF (3a) = 0.07;6a ΦF (3c;
R = cHex) = 0.026c).
The steric congestion caused by the alkyl groups of the aryl
substituents of 6b and 6c is evident from their 1H NMR spectra.
Illustrative are the three sets of resonances that are observed for
the isopropyl groups (iPr) of 6c, which is the most congested of
the three phospholes. Its para-substituent has chemical shifts
(δ(1H) = 2.90 ppm (CH); 1.29 ppm (CH3)) in the expected
range for aryl-iPr moieties, while one of the two ortho-substitu-
ents is significantly deshielded (δ(1H) = 4.85 ppm (CH); 1.60/
Increasing the substituent size on phosphorus causes a small
bathochromic shift in the lowest energy absorption for 6
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Figure 4 with the numerical values in red). Hence, increasing
the substituent size in the order phenyl (6a), mesityl (6b), isityl
(6c), and supermesityl (6d) flattens the phosphorus center,
leading to an increase in the energy of the frontier orbitals (see
also Table 2).
On planarizing the phosphorus atom, its lone pair is expected
to contribute more to the π-delocalized system, which is reflected
in the contribution of the phosphorus 3p-orbital (3p(P)) in the
HOMO. The effect for the stepwise planarization of 6a is shown
in the top of Figure 5. The equilibrium structures 6b, 6c, and 6d
have much enhanced 3p(P) participation to the HOMO of
22.5%, 25.1%, and 31.3%, respectively, as compared to 6a
(9.3%, Table 2). For the enforced fully planar system the
contribution of the 3p(P) orbital to the HOMO amounts to
37.4%. Clearly, the 3p(P) component significantly affects the
energy of the HOMO, but hardly that of the LUMO (Figure 5),
causing a decrease in band gap and enhances π-conjugation with
increasing substituent size.
The extent of conjugation appears to hardly influence the
absorption maximum, as the bathochromic shift is only 5 nm in
going from phenyl-substituted 6a to isityl-substituted 6c. This
negligible effect can be attributed to the low probability of the
HOMOfLUMO transition. Table 3 lists the time-dependent
DFT calculated transitions visible in the absorption spectrum of
6a. The transition associated for 74.3% with the HOMOfLU-
MO excitation (entry 1) has an oscillator strength (f) of only
0.08, while that for HOMOꢀ1fLUMO (65.5%), mixed with
HOMOfLUMO+2 (22.0%), (entry 3) has a much higher f of
0.13. This transition of 337.5 nm compares very well with the
Figure 4. Deformations of the phosphole ring of the P,S-bridged trans-
stilbenes 6. Planarization of the P tripod is defined by angle ϕ and P out
of C4-plane bending by angle θ. (a) phosphole side view; (b) phosphole
front view. For clarity, phosphole carbon atoms 2 and 5 are shown in
black and carbons atoms 3 and 4 in gray.
(λabs (nm): 6a 340; 6b 343; 6c 345), which suggests a decreasing
gap between the highest occupied molecular orbital (HOMO)
and the lowest unoccupied molecular orbital (LUMO). How-
ever, this trend is not reflected in the emission maxima
(Figure 3), which all lie within 3 nm (λem (nm): 6a 411; 6b 408;
6c 409). Thus, if there is a conjugative effect of the substituent
size on the phosphorus lone pair participation in the π-system,
this appears not to be reflected in the emission spectra of
phospholes 6. Puzzled by this apparent anomaly between the
spectroscopic data, we next resorted to analyzing these data with
theoretical means.
DFT Calculations of P,S-Bridged trans-Stilbenes 6. The
electronic structures of the phosphole-containing π-systems
6aꢀc, together with the sterically congested supermesityl sub-
stituted analogue 6d (Ar = 2,4,6-tri-tert-butylphenyl (Mes*)),13
were optimized using DFT with the OBPE functionals and the
TZ2P basis set (see Computational Section). These calculations
reveal two geometrical effects on increasing the size of the
P-substituent. Most obvious are the enlarging CꢀPꢀC angles,
∑(—P), causing flattening of the phosphorus, which is reflected
in the angle ϕ between the P-substituent and the phosphole CPC
plane (Figure 4; ϕ 6a 114.2ꢀ, 6b 123.1ꢀ, 6c 125.0ꢀ, 6d 129.8ꢀ).
The consequence of the planarization is an enhanced interaction
of the phosphorus lone pair with the carbon π-system. More
subtle is the effect caused by the bulk of the substituent, which
induces tilting of the phosphorus atom out of the plane formed
by the four phosphole-carbon atoms. This dihedral angle θ
(Figure 4) amounts to 6.2ꢀ for 6a and increases to 9.6ꢀ for
isityl-substituted 6c (Table 2). As such, the phosphorus lone pair
is tilted slightly toward a more parallel alignment with the carbon
based π-orbitals, causing a better overlap.
experimentally observed lowest energy absorption band at λabs
=
340 nm. Since the HOMOꢀ1 (ΔEHOMOꢀ1 = 0.34 eV) and the
LUMO (ΔELUMO = 0.21 eV) are less affected by planarization of
the phosphorus tripod on going from 6aꢀd than the HOMO
(ΔEHOMO = 0.48 eV; see Figure 5), the enhanced electronic
interaction through the π-system has little effect on the photo-
physical properties.
Oxidized P,S-Bridged trans-Stilbenes 7. Electronic devices
require fluorescent substances with high quantum yields, which
the P,S-bridged trans-stilbenes 6aꢀc do not have. Therefore the
corresponding oxides 7aꢀc were studied, as oxidation of the
phosphorus center of rigid phosphole-containing π-systems
generally enhances the fluorescence quantum yield, that is, ΦF
(3a) = 0.07 versus ΦF (3b) = 0.98.6a The desired oxides 7aꢀc were
prepared in 37ꢀ47% yield by H2O2 treatment (Scheme 2),17 as was
recently shown to be successful for phenyl-derivative 7a.8
Oxidation of the phosphorus center of 6aꢀc leads to a
significant deshielding of 31P NMR chemical shift (42.9ꢀ61.5
ppm), which is caused by the electronegative oxygen atom.
Interestingly, the trend in the relative chemical shifts for the
phosphole oxides is reversed with the phenyl-substituted 7a
having the most shielded phosphorus atom; the differences in
Δδ for 7aꢀc are much smaller than for the nonoxidized forms
(Table 1).
Of interest are the frontier orbitals, because they may assist in
analyzing the photophysical properties. To obtain insight into
the influence of the phosphorus substituent on the frontier
orbitals, we examined the forced planarization of the Cs-sym-
metry constrained 6a in steps of approximately ten degrees.16
This behavior is depicted in Figure 5, which shows that an
increased planarization of the phosphorus tripod, as indicated by
the sum of the three different CꢀPꢀC angles (∑(—P); range
290ꢀꢀ360ꢀ), pronouncedly affects the energy of the HOMO
(ΔEHOMO = 0.77 eV), but far less that of the LUMO (ΔELUMO
=
0.14 eV). The result is a significantly reduced HOMOꢀLUMO
energy gap for the planar analogue (ΔEHL = 2.19 eV) when
compared to the “pyramidal” one (ΔEHL = 2.95 eV); the
continuous decrease in ΔEHL on planarizing the phosphorus
fragment is evident in Figure 5 that gives the numerical values
(in blue) above the ∑(—P) x-axis. The relative HOMO and
LUMO energies, and thus the ΔEHL energies of the fully
optimized 6a, 6b, 6c, and 6d nicely fit the pattern for the
constrained planarization of 6a (see the highlighted bars in
UVꢀvis and Fluorescence Spectroscopy of P(O),S-Bridged
trans-Stilbenes 7. Oxidation of the phosphorus center of 6aꢀc
results in a bathochromic shift of the lowest energy absorption of
5ꢀ19 nm to λabs = 329 nm (max) and λabs = 352ꢀ364 nm (sh)
(Figure 2b), suggesting that the HOMOꢀLUMO energy gap is
reduced (Table 1).
Excitation of 7aꢀc at either one of the two absorption bands
results in a fluorescence band at λem = 408ꢀ411 nm (Figure 6),
which is, in fact, at the same wavelength as that for the
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Table 2. OPBE/TZ2P Computational Details for the Equilibrium Geometries of the Phosphole-Containing π-Conjugated
Systems 6aꢀd
compd
∑(—P)a (deg)
EHOMOb (eV)
ELUMOb(eV)
ΔEHLc (eV)
3p(P)d (%)
θ
e (deg)
6a
6b
6c
6d
303.9
316.0
319.5
324.8
0.06
0.29
0.37
0.54
2.99
3.14
3.17
3.20
2.96
2.85
2.81
2.66
9.3
6.2
8.7
9.6
6.7
22.5
25.1
31.3
a Sum of the CꢀPꢀC angles. b Relative HOMO and LUMO energies. c HOMOꢀLUMO gap. d 3p(P) contribution in the HOMO. e P bending out of
the C4-plane (Figure 4).
Table 3. Five Lowest-Energy Transitions Computed for 6a at TD-OPBE/TZ2P
entry
Ea (eV)
λb (nm)
f
c (a.u.)
main excitations (eV)d (occurrence percentage)
1
2
3
4
5
3.3895
3.4582
3.6733
3.7690
3.8240
365.8
358.5
337.5
329.0
324.2
0.0788
0.0257
0.1329
0.0584
0.0144
HOMO f LUMO (74.3)
HOMO f LUMO+1 (11.1)
HOMO f LUMO (8.2)
HOMO f LUMO+1 (88.1)
HOMOꢀ1 f LUMO (65.5)
HOMO f LUMO+2 (63.3)
HOMOꢀ1 f LUMO+1 (87.0)
HOMO f LUMO+2 (22.0)
HOMOꢀ1 f LUMO (11.8)
HOMOꢀ2 f LUMO (7.0)
a Transition energy. b Transition wavelength. c Oscillator strength. d Main excitations of the transition with relative contribution (see also Supporting
Information, Table S3).
Figure 5. Relative OPBE/TZ2P HOMO and LUMO energies (in eV) on horizontal bars for constrained 6a (black) and optimized 6aꢀd (red) versus
the sum of the CꢀPꢀC angles (∑(—P)); the corresponding HOMOꢀLUMO gaps (ΔEHL) are given in blue above the X-axes. For optimized 6aꢀd,
the HOMOꢀ1 energy levels are given at the bottom of the graph. The 3p(P) contribution to the HOMO is given in the upper part of the graph with
black squares for constrained 6a and red dots for unconstrained 6aꢀd.
corresponding λ3σ3-P analogues 6aꢀc. Evidently, the bath-
ochromic shift observed in the absorption upon oxidation is
not transferred to the fluorescence. Hence, the Stokes shift is
smaller for the oxidized species, meaning that less energy is lost
during vibrational energy relaxation. What is different for the
oxidized systems is the much higher quantum yield for
fluorescence, that is, ΦF = 0.683ꢀ0.895 for 7aꢀc versus ΦF =
0.121ꢀ0.253 for 6aꢀc. Both the smaller Stokes shift and the
higher quantum yield of the oxidized species can be rationalized
by the better overlap of the wave functions of the S0 and the S1
state. FranckꢀCondon excitation then leads to a lower occupied
vibrational level in the S1 state and thus less relaxation is needed
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Scheme 2. Oxidation of S,P-Bridged trans-Stilbenes 6aꢀc to
the Corresponding Oxides 7aꢀca
The trigonal phosphorus centers could be oxidized with H2O2
to the corresponding P(O),S-bridged trans-stilbenes 7aꢀc.
These λ5-phospholes exhibited significantly enhanced fluores-
cence quantum yields (ΦF = 0.683ꢀ0.895), while the wave-
lengths for emission remain unaffected.
This study then shows that varying the steric bulk around the
phosphorus center in extended P,S-containing π-frameworks
affects the electronic properties of the nonoxidized 6aꢀc and
the oxidized 7aꢀc. With the insight provided in this study we
hope to have contributed to elucidating the intriguing photo-
physical properties of extended π-conjugated phosphole con-
taining systems.
a a) H2O2, DCM, RT, 4ꢀ16 h.
’ EXPERIMENTAL SECTION
Computational Details. All calculations were performed using
the ADF program suite.18 Geometries were optimized using the
TZ2P basis set at the OBPE level of theory, using an integration
accuracy of 5.0 and convergence criteria of 1 ꢁ 10ꢀ5. An extensive
description of the computational results for 6 and the calibration line,
including frontier orbital pictures and coordinates, is given in the
Supporting Information.
General Remarks. All reactions are carried out under nitrogen
atmosphere using standard Schlenk techniques and dry solvents, unless
stated otherwise. 1,4-Dioxane, tetrahydrofuran (THF), and Et2O were
distilled from Na/benzophenone, TEA from CaH2, DCM from CaCl2,
and toluene from Na. Mesityl-dichlorophosphine19 and 2,4,6-triisopro-
pylphenyl-dichlorophosphine20 were prepared according to literature
procedures. 2,3-Dibromobenzo[b]thiophene (4) was prepared by a
slightly modified literature procedure.21
Figure 6. Fluorescence (solid) and excitation spectra (dotted) of
phosphole-oxide-containing π-systems 7a (red), 7b (blue), and 7c
(green) in cyclohexane (10ꢀ6 M; λexc = 350 nm; λem = 410 nm).
NMR measurements were performed on a Bruker Advance 400 or a
Bruker Advance 500. NMR chemical shifts were externally referenced to
SiMe4 (1H and 13C) or 85% H3PO4 (31P). IR spectra were recorded on a
Shimadzu FTIR-8400S, and high-resolution mass spectra were mea-
sured on a Bruker micrOTOF-Q (ESI) or a JEOL LMS-SX/SX 102 A
tandem mass spectrometer (FAB). UVꢀvis spectra are recorded at
room temperature on a Carey 300 UVꢀvisible spectrophotometer and
fluorescence spectra on a Perkin-Elmer LS50-B luminescence spectro-
meter. Spectra were recorded with a scan speed of 200 nm/min, using a
spectral width of 5 nm for both excitation and emission. Quantum yields
were determined as 10ꢀ6 M cyclohexane solutions, using perylene as
standard (ΦF = 94%).
to return to the vibrational S1 ground state. Furthermore, a better
overlap between the wave functions results in a higher probability
of radiative decay and thus a higher quantum yield.
Whereas lone pair participation cannot play a role in the
oxidized species 7aꢀc, increasing the substituent size on phos-
phorus gives, like 6aꢀc, a small bathochromic shift for the lowest
energy absorption, that is, λabs 7a = 352, 7b = 353, and 7c =
364 nm. In analogy with the nonoxidized species 6aꢀc, this trend
is not reflected in the emission maxima, which are at
408ꢀ411 nm within 3 nm of each other.
’ CONCLUSION
The P-substituted ladder-type P,S-bridged trans-stilbenes
6aꢀc have been synthesized successfully. They exhibit intense
emissions in the blue region (λem = 408ꢀ411 nm; ΦF
=
0.121ꢀ0.253). The influence of the size of the phosphorus
substituent on the geometry and photophysical properties of
the conjugated π-system was studied. DFT calculations revealed
that increasing the bulkiness of the substituent results in a
flattening of the pyramidal phosphorus, increased participation
of its lone pair in the π-delocalization, and a decrease of the
HOMOꢀLUMO gap. A larger contribution of the lone pair of
phosphorus in the π-system raises the HOMO energy, while
leaving the LUMO virtually unaffected. The more shielded 31P
NMR chemical shifts of the trigonal phosphorus nucleus of 6aꢀc
are attributed to steric influence of the more bulky substituents.
Yet, these electronic effects are hardly expressed in the optical
properties, apart from a small bathochromic shift of the lowest
energy absorption as the substituent gets bigger. The reason is
that the transition responsible for the lower energy absorption of
6a is mainly associated with the HOMOꢀ1fLUMO excitation.
2,3-Dibromobenzo[b]thiophene (4).21 NBS (46.4 g, 260
mmol, 2.5 equiv) was added in small portions over a period of 1 h to
a solution of benzo[b]thiophene (14.0 g, 104 mmol, 1 equiv) in DCM/
acetic acid (1/1 (v/v), 820 mL) at 0 ꢀC. The color of the reaction
mixture changed from yellow to red and stirring was continued at room
temperature. The progress of the reaction was checked by aqueous
workup of small aliquots of the reaction mixture. To speed up the
reaction, three portions of NBS were added to the reaction mixture at t =
17 h (18.5 g, 104 mmol), t = 89 h (5.56 g, 31.2 mmol), and at t = 5 days
(4.26 g, 23.9 mmol). After 8 days of stirring, the reaction mixture was
washed subsequently with 10% KOH (aq), 5% NaHCO3 (aq), 5%
Na2S2O3 (aq), and water. The organic phase was dried over MgSO4,
filtered, and all volatiles were removed in vacuo. The yellow residue was
subjected to column chromatography over silica gel eluting with hexane
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to obtain 4 as a white solid (24.8 g, 84.8 mmol, 82%). 1H NMR (CDCl3;
250.13 MHz): δ (ppm) = 7.74 (d, 3JHH = 7.4 Hz, 1H, H4); 7.73 (dd,
dropwise over a period of 30 min to a solution of 3-bromo-2-(2-
bromophenyl)benzo[b]thiophene (185 mg, 503 μmol, 1 equiv) in
Et2O (10 mL) at ꢀ78 ꢀC. The reaction mixture was stirred for
30 min at ꢀ78 ꢀC and was then slowly warmed to room temperature
over a period of 1.5 h. MesPCl2 (111 mg, 503 μmol, 1 equiv) was slowly
added dropwise to the light yellow turbid reaction mixture over a period
of 20 min. Stirring was continued for 3 h, during which the reaction
mixture turned slightly darker. The solvent was removed in vacuo, and
the residue was extracted into Et2O. After removal of the solvent in
vacuo, the crude product was subjected to column chromatography over
Al2O3 eluting with hexane and subsequently with hexane/DCM 1/1 (RF
(hexane) = 0.35), which afforded 6b as a white solid (143 mg, 398 μmol,
79%). 1H NMR (CDCl3; 400.13 MHz): δ (ppm) = 7.89 (d, 3JHH = 7.2
Hz, 1H, H9); 7.74 (d, 3JHH = 8.0 Hz, 1H, H6); 7.64 (dd, 3JHH = 7.2 Hz,
3JHP = 4.8 Hz, 1H, H1); 7.52 (dd, 3JHH = 7.2 Hz, 4JHH = 2.0 Hz, 1H, H4);
7.44 (t, 3JHH = 7.2 Hz, 1H, H3); 7.26ꢀ7.32 (m, 3H, H2, H7, H8); 7.05
(bs, 1H, m-MesH); 6.62 (bs, 1H, m-MesH); 3.07 (bs, 3H, o-CH3-ArP);
2.25 (s, 3H, p-CH3-ArP); 1.26 (bs, 3H, o-CH3-ArP). 13C NMR (CDCl3;
100.62 MHz): δ (ppm) = 145.1ꢀ145.3 (m, C4a, C4b, 2x o-ArP); 142.8
3JHH = 7.1 Hz, 4JHH = 1.5 Hz, 1H, H7); 7.43 (dt, 3JHH = 7.6 Hz, 4JHH
1.5 Hz, 1H, H5); 7.38 (dt, 3JHH = 7.0 Hz, 4JHH = 1.4 Hz, 1H, H6).
=
3-Bromo-2-(2-bromophenyl)benzo[b]thiophene (5). 2,3-
Dibromobenzo[b]thiophene (2.13 g, 7.34 mmol, 1 equiv), 2-bromo-
phenyl boronic acid (1.47 g, 7.34 mmol, 1 equiv), and Pd(PPh3)4 (424
mg, 367 μmol, 5 mol %) were dissolved in 1,4-dioxane (75 mL), and
degassed 2 M Na2CO3 (aq; 15 mL) was added. The yellow reaction
mixture was refluxed for 16 h, after which the solvent was removed. The
residue was redissolved in DCM and washed with water. The organic
layer was dried over MgSO4, filtered, and the solvent was removed in
vacuo. The yellow residue was purified by column chromatography over
silica gel eluting with hexane (RF = 0.26) and resulted in 5 as a white solid
(2.48 g, 6.74 mmol, 92%). Mp: 72.5ꢀ73.3 ꢀC. 1H NMR (CDCl3; 400.13
MHz): δ (ppm) = 7.88 (dd, 3JHH = 7.8 Hz, 4JHH = 1.4 Hz, 1H, H4); 7.84
(dd, 3JHH = 7.8 Hz, 4JHH = 1.1 Hz, 1H, H7); 7.73 (dd, 3JHH = 8.0 Hz,
0
4JHH = 1.1 Hz, 1H, H6 ); 7.50 (dt, 3JHH = 7.8 Hz, 4JHH = 1.1 Hz, 1H, H5);
0
7.45 (dd, 3JHH = 7.4 Hz, 4JHH = 2.0 Hz, 1H, H3 ); 7.44 (dt, 3JHH = 7.8 Hz,
0
(d, 1JCP = 5.2 Hz, C9b); 140.5 (d, 4JCP = 1.5 Hz, p-ArP); 139.1 (d, 1JCP
=
4JHH = 1.4 Hz, 1H, H6); 7.42 (dt, 3JHH = 7.4 Hz, 4JHH = 1.1 Hz, 1H, H4 );
0
5.4 Hz, C10a); 138.3 (d, 2JCP = 8.0 Hz, C9a); 137.9 (d, 3JCP = 17.1 Hz,
C5a); 130.0 (bs, m-ArP); 129.5 (d, 2JCP = 20.6 Hz, C1); 127.6 (s, C3);
125.9 (d, 3JCP = 8.0 Hz, C2); 124.6 (s, C7); 124.3 (s, C8); 123.4 (s, C9);
122.8 (s, C6); 121.8 (s, C4); 20.9 (s, p-CH3ꢀArP), 18.9 (bs, o-
7.33 (ddd, 3JHH = 8.0 Hz, 3JHH = 7.4 Hz, 4JHH = 2.0 Hz, 1H, H5 ). 13
C
NMR (CDCl3; 62.90 MHz): δ (ppm) = 138.4 (s, C7a); 137.8 (s, C3a);
0
0
0
0
137.2 (s, C1 ); 134.1 (s, C2); 133.0 (s, C6 ); 132.5 (s, C3 ); 130.6 (s, C5 );
0
0
127.1 (s, C4 ); 125.6 (s, C6); 125.2 (s, C5); 124.5 (s, C2 ); 123.6 (s, C4);
122.2 (s, C7); 108.5 (s, C3). HR-MS (FAB): calcd for C14H879Br81BrS:
367.8693, found: 367.8695. m/z (%): 370 (54) [M (81Br)2]+, 368 (100)
[M (79Br81Br)]+, 366 (50) [M (79Br)2]+, 208 (40) [Mꢀ Br2]+. IR(neat):
ν (cmꢀ1) = 3067 (w); 1462 (m); 1433 (m); 1420 (m); 1321 (w); 1308
(w); 1254 (m); 1051 (w); 1018 (m); 976(w); 887 (m); 799 (w);746 (s);
727 (m); 683 (m); 644 (w); 621 (w); 584 (w); 500 (w); 444 (m).
10-Phenyl-10H-benzo[b]phosphindolo[2,3-d]thiophene
(6a). n-BuLi (1.6 M in hexane, 2.75 mL, 4.40 mmol, 2.2 equiv) was
added dropwise over a period of 45 min to a solution of 3-bromo-2-(2-
bromophenyl)benzo[b]thiophene (737 mg, 2.00 mmol, 1 equiv) in
Et2O (40 mL) at ꢀ78 ꢀC. The reaction mixture was stirred for 30 min at
ꢀ78 ꢀC and was then slowly warmed to room temperature over a period
of 1.5 h. PhPCl2 (270 μL, 2.00 mmol, 1 equiv) was slowly added
dropwise to the light yellow turbid reaction mixture over a period of 30
min. Stirring was continued for 3 h, during which the reaction mixture
turned slightly darker. The solvent was removed in vacuo, and the
residue was extracted into Et2O. After removal of the solvent in vacuo,
the crude product was purified by column chromatography over Al2O3
eluting with DCM (RF = 0.65), which resulted in 6a as a yellow solid
(632 mg, 2.00 mmol, 100%). 1H NMR(CDCl3; 400.13 MHz): δ(ppm) =
7.93 (m, 3JHH = 8.7 Hz, 1H, H9); 7.75 (m, 1H, H6); 7.73 (d, 3JHH = 7.5 Hz,
3
CH3ꢀArP), 13.9 (d, JCP = 20.2 Hz, o-CH3ꢀArP). The signal for
ipso-ArP is unresolved. 31P NMR (CDCl3; 161.98 MHz): δ (ppm) =
ꢀ29.7 (s). HR-MS (FAB): calcd for C23H20PS (M + H): 359.1023,
found: 359.1024. m/z (%): 359 (75) [M + H]+, 358 (91) [M]+, 239 (100)
[Mꢀ Mes]+. UVꢀvis (DCM): λ(nm) =236(ε=9.40ꢁ 104 Mꢀ1 cmꢀ1);
303 (ε=4.71ꢁ 104 Mꢀ1 cmꢀ1); 310 (ε=4.64ꢁ 104 Mꢀ1 cmꢀ1);343(sh,
ε = 2.13 ꢁ 104 Mꢀ1 cmꢀ1). FS (cHex): λ (nm) = 408 (ΦF = 0.121).
10-(2,4,6-Triisopropylphenyl)-10H-benzo[b]phosphindolo-
[2,3-d]thiophene (6c). n-BuLi (1.6 M in hexane, 1.60 mL, 2.55 mmol,
2.2 equiv) was added dropwise over a period of 30 min to a solution of
3-bromo-2-(2-bromophenyl)benzo[b]thiophene (426 mg, 1.16 mmol,
1 equiv) in Et2O (23 mL) at ꢀ78 ꢀC. The reaction mixture was stirred
for 30 min at ꢀ78 ꢀC and was then slowly warmed to room temperature
over a period of 1.5 h. IsPCl2 (0.35 M in Et2O, 3.32 mL, 116 mmol,
1 equiv) was slowly added dropwise to the light yellow turbid reaction
mixture over a period of 45 min. Stirring was continued for 16 h, during
which the reaction mixture turned slightly darker. The solvent was
removed in vacuo, and the residue was extracted into a mixture of Et2O
and DCM. After removal of the solvent in vacuo, the crude product was
purified by column chromatography over Al2O3 eluting with hexane and
subsequently with hexane/DCM 1/1 (RF (hexane) = 0.31), which
1
1H, H4); 7.72 (dd, 3JHH = 7.5 Hz, 3JHP = 5.1 Hz, 1H, H1); 7.47 (dt, 3JHH
=
afforded 6c as a yellow solid (516 mg, 1.16 mmol, 100%). H NMR
(CDCl3; 400.13 MHz): δ (ppm) = 7.89 (d, 3JHH = 8.0 Hz, 1H, H9); 7.81
(d, 3JHH = 7.8 Hz, 1H, H6); 7.68 (dd, 3JHH = 7.5 Hz, 3JHP = 5.0 Hz, 1H,
H1); 7.55 (dd, 3JHH = 7.3 Hz, 4JHH = 1.7 Hz, 1H, H4); 7.45 (t, 3JHH = 7.3
Hz, 1H, H3); 7.32 (dt, 3JHH = 7.3 Hz, 4JHH = 1.7 Hz, 1H, H2); 7.27ꢀ7.31
(m, 2H, H7, H8); 7.21 (dd, 4JHP = 5.6 Hz, 4JHH = 1.6 Hz, 1H, m-IsH); 6.82
(d, 4JHH = 1.6 Hz, 1H, m-IsH); 4.85 (sept, 3JHH = 6.8 Hz, 1H, o-(CH3)2-
CH-ArP); 2.90 (sept, 3JHH = 6.8 Hz, 1H, o-(CH3)2CH-ArP); 1.91 (sept,
7.5 Hz, 4JHH = 1.2 Hz, 1H, H3); 7.41 (dt, 3JHH = 8.3 Hz, 3JHP = 1.6 Hz, 2H,
o-PhH); 7.36 (m, 2H; H7, H8); 7.32 (dt, 3JHH = 7.5 Hz, 4JHP = 2.5 Hz, 1H,
H2); 7.31 (m, 1H, p-PhH); 7.27 (t, 3JHH = 7.2 Hz, 2H, m-PhH). 13C NMR
(CDCl3; 100.62 MHz): δ (ppm) = 148.2 (d, 2JCP = 3.8Hz, C4b); 145.9 (d,
2JCP = 4.2 Hz, C4a); 142.9 (d, 1JCP = 4.2 Hz, C9b); 139.5 (d, 1JCP = 2.2 Hz,
C
10a); 138.1 (d, 2JCP = 8.1 Hz, C9a); 138.0 (d, 3JCP = 17.0 Hz, C5a); 133.8
(d, 1JCP = 16.9 Hz, ipso-PhP); 132.7 (d, 2JCP = 20.9 Hz, o-PhP); 130.1 (d,
2JCP = 21.5 Hz, C1); 129.4 (d, 4JCP = 0.7 Hz, p-PhP); 128.7 (d, 3JCP = 7.8
Hz, m-PhP); 128.6 (s, C3); 126.7 (d, 3JCP = 6.2 Hz, C2); 124.9 (s, C7);
124.4 (s, C8); 123.5 (s, C9); 122.9 (s, C6); 121.6 (s, C4). 31P NMR
(CDCl3; 161.98 MHz): δ (ppm) = ꢀ17.4 (s). HR-MS (FAB): calcd for
C20H14PS (M + H): 317.0554, found: 317.0554. m/z (%): 317 (43) [M +
H]+, 316 (49) [M]+, 2ꢀ319 (100) [M ꢀ Ph]+. UVꢀvis (DCM)ꢀ: 1λ (nm) =
230 (ε = 4.75 ꢁ 104 M cmꢀ1); 260 (ε = 2.93 ꢁ 104 Mꢀ1 cm ); 316 (ε
= 1.80 ꢁ 104 Mꢀ1 cmꢀ1); 340 (sh, ε = 1.21 ꢁ 104 Mꢀ1 cmꢀ1). FS
(cHex): λ (nm) = 411; ΦF = 0.253.
3
3JHH = 6.8 Hz, 1H, p-(CH3)2CH-ArP); 1.60 (d, JHH = 6.9 Hz, 3H,
o-(CH3)2CH-ArP); 1.54 (d, 3JHH = 6.9 Hz, 3H, o-(CH3)2CH-ArP); 1.29
(d, 3JHH = 6.8 Hz, 6H, p-(CH3)2CH-ArP); 0.44 (d, 3JHH = 6.8 Hz, 3H,
o-(CH3)2CH-ArP); 0.31 (d, 3JHH = 6.8 Hz, 3H, o-(CH3)2CH-ArP). 13
C
NMR (CDCl3; 100.62 MHz): δ (ppm) = 157.8 (d, 2JCP = 36.1 Hz, o-Is);
156.9 (d, 2JCP =5.2 Hz, o-Is); 151.9 (d, 4JCP =1.3 Hz, p-Is);147.7 (d, 2JCP
=
1.3 Hz, C4b); 144.2 (d, 2JCP = 11.1 Hz, C4a); 142.8 (d, 1JCP = 5.6 Hz, C9b);
141.3 (d, 1JCP = 8.6 Hz, C10a); 138.3 (d, 2JCP = 6.1 Hz, C9a); 138.1 (d, 3JCP
= 17.1 Hz, C5a); 129.3 (d, 2JCP = 20.1 Hz, C1); 127.4 (s, C3); 125.5 (s, C7);
124.7 (s, C8); 124.3 (s, C2); 123.5 (s, C9); 122.9 (s, C4); 122.70 (s, m-Is);
122.69 (d, 1JCP = 57.6 Hz, ipso-Is); 122.2 (s, C6); 121.8 (d, 3JCP = 8.8 Hz,
10-Mesityl-10H-benzo[b]phosphindolo[2,3-d]thiophene
(6b). n-BuLi (1.6 M in hexane, 700 μL, 1.12 mmol, 2.2 equiv) was added
8521
dx.doi.org/10.1021/ic201116p |Inorg. Chem. 2011, 50, 8516–8523

Inorganic Chemistry
ARTICLE
m-Is); 34.2 (s, p-(CH3)2CH-ArP); 33.0 (d, 3JCP = 38.0 Hz, o-(CH3)2CH-
ArP); 29.3 (s, o-(CH3)2CH-ArP); 25.4 (s, o-(CH3)2CH-ArP); 24.7 (s,
o-(CH3)2CH-ArP); 23.9 (s, o-(CH3)2CH-ArP); 23.7 (s, p-(CH3)2CH-
ArP); 23.3 (s, o-(CH3)2CH-ArP). 31P NMR (CDCl3; 161.98 MHz):
δ(ppm) = ꢀ33.4 (s). HR-MS (FAB): calcdfor C29H32PS: 443.1962 (M +
H), found: 443.1960. m/z (%): 443 (73) [M + H]+, 442 (100) [M]+,
239 (44) [M ꢀ Is]+. UVꢀvis (DCM): λ (nm) = 230 (ε = 4.55 ꢁ
104 Mꢀ1 cmꢀ1); 259 (ε = 2.99 ꢁ 104 Mꢀ1 cmꢀ1); 302 (ε = 2.00 ꢁ
104 Mꢀ1 cmꢀ1); 324 (ε = 1.66 ꢁ 104 Mꢀ1 cmꢀ1); 345 (sh, ε = 9.04 ꢁ
103 Mꢀ1 cmꢀ1). FS (cHex): λ (nm) = 409; ΦF = 0.154.
(s, p-CH3ꢀArP); 14.1 (s, o-CH3ꢀArP). 31P NMR (CDCl3; 161.98
MHz): δ (ppm) = 27.4 (s). HR-MS (ESI): calcd for C23H20OPS
(M + H): 375.0972, found: 375.0967. m/z (%): 375 (100) [M + H]+.
IR (neat): ν (cmꢀ1) = 3298 (w); 2959 (w); 2924 (w); 2855 (w);
1640 (w); 1412 (m); 1261 (m); 1018 (w); 872 (w); 799 (s); 694 (w);
451 (m). UVꢀvis (DCM): λ (nm) = 229 (sh, ε = 1.64 ꢁ 104
M
M
ꢀ1 cmꢀ1); 257 (ε = 1.35 ꢁ 104 Mꢀ1 cmꢀ1); 269 (sh, ε = 9.96 ꢁ 103
ꢀ1 cmꢀ1); 304 (ε = 4.44 ꢁ 103 Mꢀ1 cmꢀ1); 329 (ε = 3.33 ꢁ 103
Mꢀ1 cmꢀ1); 353 (sh, ε = 2.42 ꢁ 103 Mꢀ1 cmꢀ1). FS (cHex): λ
(nm) = 409; ΦF = 0.895.
10-(2,4,6-Triisopropylphenyl)-10H-benzo[b]oxophosphin-
dolo[2,3-d]thiophene (7c). H2O2 (56 μL, 2.32 mmol, 6 equiv) was
added slowly to a solution of 6c (172 mg, 386 μmol, 1 equiv) in DCM
(10 mL). After 16 h of stirring, the reaction was complete, and a few drops
of water were added to the reaction mixture. The solution was dried over
MgSO4, filtered, and the solvent was removed in vacuo. The yellowish
residue was subjected to column chromatography over Al2O3 eluting with
DCM and subsequently with DCM/MeOH (95/5) (RF (DCM) = 0.12)
to obtain 7c as a white solid (64.2 mg, 140 μmol, 36%). Mp: 112.6ꢀ
113.1 ꢀC. 1H NMR (CDCl3; 400.13 MHz): δ (ppm) = 7.84ꢀ7.87 (m,
1H, H9); 7.68ꢀ7.73 (m, 1H, H6); 7.64 (dd, 3JHP = 10.6 Hz, 3JHH = 7.4 Hz,
10-Phenyl-10H-benzo[b]oxophosphindolo[2,3-d]thiophene
(7a). H2O2 (44μL, 1.80 mmol, 6 equiv) was added slowly to a solution of 6a
(94.9 mg, 300 μmol, 1 equiv) in DCM (10 mL). After 4 h of stirring, the
reaction was complete, and a few drops of water were added to the reaction
mixture. The solution was dried over MgSO4, filtered, and the solvent was
removed in vacuo. The yellowish residue was subjected to column chroma-
tography over Al2O3 eluting with DCM and subsequently with DCM/
MeOH (98/2) (RF (DCM) = 0.05) to obtain 7a as a white solid (46.6 mg,
140 μmol, 47%). Mp: 160.8ꢀ161.3 ꢀC. 1H NMR (CDCl3; 400.13 MHz):
δ (ppm) = 7.83ꢀ7.86 (m, 3JHH = 7.2 Hz, 1H, H9); 7.78ꢀ7.81 (m, 1H, H6);
7.73ꢀ7.78 (m, 2H, H2, H3); 7.67 (dd, 3JHP = 10.4 Hz, 3JHH = 7.2 Hz, 1H,
H1); 7.50ꢀ7.52 (m, 2H, o-PhH); 7.48 (dd, 3JHH = 7.2 Hz, 4JHH = 2.0 Hz,
1H, H4); 7.35ꢀ7.41 (m, 2H, H7, H8); 7.29ꢀ7.34 (m, 3H, m-PhH, p-PhH).
13C NMR (CDCl3; 100.62 MHz): δ (ppm) = 154.5 (d, 2JCP = 18.1 Hz,
C4b); 143.1 (d, 2JCP = 12.1 Hz, C4a); 137.4 (d, 2JCP = 19.1 Hz, C9a); 136.6 (d,
1JCP = 101.6 Hz, C10a);136.0 (d, 3JCP =5.0 Hz, C5a); 133.0 (d, 4JCP =2.0 Hz,
p-PhP); 132.3 (d, 2JCP = 2.9 Hz, C1); 130.8 (d, 3JCP = 11.2 Hz, m-PhP);
130.7 (d, 1JCP = 78.4 Hz, ipso-PhP); 129.6 (d, 1JCP = 108.9 Hz, C9b); 129.4
(d, 4JCP = 4.2 Hz, C3); 129.3 (d, 3JCP = 5.7 Hz, C2); 128.8 (d, 2JCP = 12.9 Hz,
o-PhP); 125.9 (s, C7); 125.4 (s, C8); 123.33 (s, C9); 123.27 (s, C6); 121.8 (d,
3JCP = 9.1 Hz, C4). 31P NMR (CDCl3; 161.98 MHz): δ (ppm) = 25.5 (s).
HR-MS (ESI): calcd for C20H13OPSNa (M + Na): 355.0322, found:
355.0317. m/z (%): 355 (100) [M + Na]+. IR (neat): ν (cmꢀ1) = 3391
(w); 3055 (w); 2920 (w); 2856 (w); 1589 (w); 1458 (w); 1435 (w); 1420
(w); 1312 (w); 1261 (w); 1192 (m); 1107 (m); 1022 (m); 790 (m);
748 (s); 721 (m); 709 (m); 690 (m); 633 (m); 524 (s); 428 (m). UVꢀvis
(DCM): λ (nm) = 260 (ε = 1.73 ꢁ 104 Mꢀ1 cmꢀ1); 268 (sh, ε = 1.44 ꢁ
104 Mꢀ1 cmꢀ1); 302 (ε = 5.52 ꢁ 103 Mꢀ1 cmꢀ1); 330 (ε = 3.20 ꢁ 103
1H, H1); 7.53(dd, 3JHH = 7.4 Hz, 4JHP = 3.2 Hz, 1H, H4); 7.49 (dd, 3JHH
=
7.4 Hz, 4JHH = 1.3 Hz, 1H, H3); 7.35 (ddd, 3JHH = 7.3 Hz, 4JHP = 3.7 Hz,
4JHH = 1.3 Hz, 1H, H2); 7.29ꢀ7.33 (m, 2H, H7, H8); 7.11 (d, 4JHP = 4.0
3
Hz, 2H, m-IsH); 2.88 (sept, JHH = 6.9 Hz, 1H, p-(CH3)2CH-ArP);
3
1.16ꢀ1.34 (m, 2H, o-(CH3)2CH-ArP); 1.25 (dd, JHH = 6.9 Hz, 3H,
3
p-(CH3)2CH-ArP); 1.02 (bd, JHH = 6.4 Hz, 3H, o-(CH3)2CH-ArP);
3
0.93 (bd, JHH = 6.4 Hz, 3H, o-(CH3)2CH-ArP). 13C NMR (CDCl3;
100.62 MHz): δ (ppm) = 152.8 (d, 4JCP = 2.8 Hz, p-Is); 152.6 (d, 2JCP
=
25.4 Hz, C4b); 147.7 (s, o-Is); 143.2 (d, 2JCP = 11.8 Hz, C9a); 140.3 (d,
1JCP = 107.7 Hz, C10a); 138.7 (s, o-Is); 136.7 (d, 2JCP = 17.4 Hz, C4a);
136.1 (d, 3JCP = 13.0 Hz, C5a); 134.8 (d, 1JCP = 105.0 Hz, C9b); 132.4 (d,
4JCP = 2.0 Hz, C3); 129.3 (d, 3JCP = 11.3 Hz, C2); 128.5 (d, 2JCP = 10.2 Hz,
C1); 125.8 (s, C7); 125.2 (s, C8); 123.38 (s, C9); 123.35 (s, m-Is); 123.26
(s, C6); 122.2 (d, 3JCP = 8.7 Hz, C4); 119.0 (d, 1JCP = 102.4 Hz, ipso-Is);
34.1 (s, p-(CH3)2CH-ArP); 30.1 (s, o-(CH3)2CH-ArP); 30.0 (s,
o-(CH3)2CH-ArP); 24.9 (bs, o-(CH3)2CH-ArP); 24.5 (bs, o-(CH3)2-
CH-ArP); 23.6 (s, p-(CH3)2CH-ArP). 31P NMR (CDCl3; 161.98 MHz):
δ (ppm) = 28.1 (s). HR-MS (FAB): calcd for C29H32OPS (M + H):
459.1911, found: 459.1909. m/z (%): 459 (100) [M + H]+, 255 (18) [M
ꢀ Is]+, 239 (11) [M ꢀ OIs]+. IR (neat): ν (cmꢀ1) = 2959(w);2924(w);
2866 (w); 1601 (w); 1462 (w); 1416 (w); 1312 (w); 1261 (m); 1184 (m);
1072 (s); 1018 (s); 941 (w); 880 (w); 795 (s); 752 (s); 718 (m); 675 (m);
648 (m); 521 (s); 490 (m); 451 (m). UVꢀvis (DCM): λ (nm) = 233 (ε =
2.49 ꢁ 104 Mꢀ1 cmꢀ1); 264 (ε = 2.76 ꢁ 104 Mꢀ1 cmꢀ1); 271 (sh, ε =
2.45 ꢁ 104 Mꢀ1 cmꢀ1); 329 (ε = 4.92 ꢁ 103 Mꢀ1 cmꢀ1); 364 (sh, ε =
2.57 ꢁ 103 Mꢀ1 cmꢀ1). FS (cHex): λ (nm) = 408; ΦF = 0.683.
M
ꢀ1 cmꢀ1); 352 (sh, ε = 2.77 ꢁ 103 Mꢀ1 cmꢀ1). FS (cHex): λ (nm) =
411; ΦF = 0.837.
10-Mesityl-10H-benzo[b]oxophosphindolo[2,3-d]thio-
phene (7b). H2O2 (19 μL, 797 μmol, 6 equiv) was added slowly to
a solution of 6b (47.6 mg, 133 μmol, 1 equiv) in DCM (4 mL). After
6 h of stirring, the reaction was complete, and a few drops of water
were added to the reaction mixture. The solution was dried over
MgSO4, filtered, and the solvent was removed in vacuo. The
yellowish residue was subjected to column chromatography over
Al2O3 eluting with DCM and subsequently with DCM/MeOH
(95/5) (RF (95/5) = 0.59) to obtain 7b as a white solid (22.4 mg,
’ ASSOCIATED CONTENT
1
59.8 μmol, 45%). Mp: 110.3ꢀ112.5 ꢀC. H NMR (CDCl3; 400.13
MHz): δ (ppm) = 7.85ꢀ788 (m, 1H, H9); 7.68ꢀ7.72 (m, 1H, H6);
7.64 (dd, 3JHP = 10.4 Hz, 3JHH = 7.2 Hz, 1H, H1); 7.50ꢀ7.54 (m, 2H,
S
Supporting Information. An extensive description of the
b
computational results for 6 and the calibration line, including
frontier orbital pictures and coordinates. This material is available
free of charge via the Internet at http://pubs.acs.org.
3
4
H3, H4); 7.35 (dd, JHH = 7.34 Hz, JHP = 3.4 Hz, 1H, H2);
7.31ꢀ7.35 (m, 2H, H7, H8); 6.88 (d, 4JHP = 3.6 Hz, 2H, m-MesH);
2.27 (s, 3H, p-CH3-ArP); 1.43 (s, 3H, o-CH3-ArP); 0.88 (s, 3H, o-
CH3-ArP). 13C NMR (CDCl3; 125.80 MHz): δ (ppm) = 154.0 (d,
2JCP = 26.2 Hz, C4b); 143.2 (d, 2JCP = 12.1 Hz, C9a); 142.04 (s, p-ArP
’ AUTHOR INFORMATION
1
Corresponding Author
*E-mail: k.lammertsma@vu.nl.
or o-ArP); 142.02 (s, p-ArP or o-ArP); 138.4 (d, JCP = 107.3 Hz,
C
10a); 137.4 (d, 2JCP = 18.0 Hz, C4a); 136.1 (d, 3JCP = 13.0 Hz, C5a);
132.7 (d, 4JCP = 2.1 Hz, C3); 132.6 (d, 1JCP = 105.4 Hz, C9b); 132.4
(s, o-ArP); 131.5 (d, 3JCP = 12.1 Hz, m-ArP); 129.5 (d, 3JCP = 11.2
Hz, C2); 128.8 (d, 2JCP = 10.1 Hz, C1); 125.9 (s, C7); 125.3 (s, C8);
’ ACKNOWLEDGMENT
123.43 (s, C6); 123.41 (s, C9); 122.1 (d, JCP = 8.7 Hz, C4); 121.3
(d, JCP = 102.3 Hz, ipso-ArP); 30.3 (s, o-CH3ꢀArP); 21.0
3
This work benefitted from interactions within the European
PhoSciNet (CM0802).
1
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Inorganic Chemistry
ARTICLE
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